KR20140052064A - Process for oxidizing alkyl-aromatic compounds - Google Patents

Abstract

The present invention relates to a process for the oxidation of alkyl-aromatics. The method comprises: an oxidation step of oxidizing an alkyl-aromatic compound to produce a first oxidation product; Contacting at least a portion of the first oxidation product with a solvent comprising an ionic liquid, a bromine source, a catalyst, and an oxidizing agent to form a second solution comprising an aromatic alcohol, an aromatic aldehyde, an aromatic ketone, and an aromatic carboxylic acid, And a contact step of producing an oxidation product.

Description

PROCESS FOR OXIDIZING ALKYL-AROMATIC COMPOUNDS [0002]

Priority Claim for Initial National Application

This application claims priority from U.S. Patent Application No. 13 / 340,253, filed December 29, 2011.

Technical field

The present invention relates to a process for the oxidation of alkyl-aromatics. More specifically, the present invention relates to a method of oxidizing an alkyl-aromatic compound having a post-oxidation reaction.

Oxidation of alkylaromatics, such as toluene and xylene, is an important commercial process. A variety of oxidation products can be obtained, including aromatic carboxylic acids such as terephthalic acid (1,4-benzenedicarboxylic acid) and isophthalic acid (1,3-benzenedicarboxylic acid) Is used.

It is known that oxidation products, such as aromatic alcohols, aromatic aldehydes, aromatic ketones, and aromatic carboxylic acids, may solidify or crystallize under oxidizing conditions and / or as the reaction mixture cools. Thus, a mixture of oxidation products requiring additional treatment to increase the purity of a given product can be prepared. For example, in the preparation of terephthalic acid, the oxidation product is often referred to as crude terephthalic acid, which means that the oxidation product reacts with the color body and the intermediate oxidation product, especially 4-carboxybenzaldehyde (4-CBA) Because it contains impurities. To obtain polymer grade or purified terephthalic acid, various purification steps are known in the art including the following steps: washing the crude terephthalic acid with water and / or solvent, additional oxidation or crystallization steps, and usually palladium and Reacting a solution of crude terephthalic acid dissolved in hydrogenation conditions comprising a carbon containing catalyst with hydrogen. Often a number of purification steps are used.

US 2,833,816 discloses a process for oxidizing an aromatic compound to the corresponding aromatic carboxylic acid. The liquid phase oxidation method of an alkylaromatic compound uses molecular oxygen, metal or metal ion, and bromine or bromide ion in the presence of an acid. The metal may comprise cobalt and / or manganese. Exemplary acids include lower aliphatic monocarboxylic acids containing from 1 to 8 carbon atoms, especially acetic acid.

US 6,355,835 discloses a process for preparing benzene dicarboxylic acids by liquid oxidation of xylene isomers using oxygen or air by oxidation in the presence of acetic acid as solvent, cobalt salt as catalyst and initiator. Following the oxidation step, flashing of the reaction mixture to remove volatiles and cooling of the material to obtain crude benzene di-carboxylic acid and filtrate as a solid product and filtration are carried out. Recrystallization of the crude benzene di-carboxylic acid to obtain a purity of 99% or more and recycling of the filtrate are also disclosed.

US 7,094,925 discloses a process for preparing alkyl-aromatic compounds. The method includes mixing an oxidizing agent or a sulfur compound in the presence of an ionic liquid. Any other form of air, dioxygen, peroxide, superoxide, or active oxygen, nitrite, nitrate, and other oxides or oxyhalides of nitric acid or nitrogen (hydrates or anhydrides) have. The process is usually carried out under Bronsted acidic conditions. The oxidation is preferably carried out in an ionic liquid containing an acid promoter, such as methanesulfonic acid. The product is preferably an intermediate compound of a carboxylic acid or ketone or an oxidizing agent, such as an aldehyde, or an alcohol.

US 7,985,875 describes a process for preparing aromatic polycarboxylic acids by liquid phase oxidation of bis- or tri-substituted benzene or naphthalene compounds. The method comprises contacting an aromatic compound with an oxidizing agent in the presence of a carboxylic acid solvent, a metal catalyst, and a promoter in a reaction zone. The promoter is an ionic liquid comprising an organic cation and a bromide anion or an iodide anion. The promoter is used in a concentration range of 10 to 50,000 ppm (based on the solvent), preferably in a concentration range of 10 to 1,000 ppm. Other promoters, such as bromine containing compounds, need not be used in this method. The process produces crude terephthalic acid (CTA) with 1.4-2.2% 4-CBA. Purification of CTA is required to obtain purified terephthalic acid (PTA).

US 2010/0174111 describes a process for purifying arylcarboxylic acids, such as terephthalic acid. The non-pure acid dissolves or disperses in the ionic liquid. The non-solvent (defined as a molecular solvent in which the ionic solvent has a high solubility and the aryl carboxylic acid has little or no solubility) is added to the solution to precipitate the purified acid.

US 7,692,036, US 2007/0155985, US 2007/0208193, and US 2010/0200804 disclose a method and apparatus for performing liquid phase oxidation of an oxidizing compound. Liquid phase oxidation is carried out in a bubble column reactor which provides high efficiency reactions at relatively low temperatures. When the oxidized compound is p-xylene, the product of the oxidation reaction is CTA which must be purified. Tablets are known to be easier than conventional high temperature processes.

One aspect of the invention is a method of oxidizing an alkyl-aromatic compound. In one embodiment, the method comprises: an oxidation step of oxidizing an alkyl-aromatic compound to produce a first oxidation product; Contacting at least a portion of the first oxidation product with a solvent comprising an ionic liquid, a bromine source, a catalyst, and an oxidizing agent to form a second solution comprising an aromatic alcohol, an aromatic aldehyde, an aromatic ketone, and an aromatic carboxylic acid, And a contact step of producing an oxidation product.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a general process flow diagram of an embodiment of a process for preparing a purified alkylaromatic aromatic compound.

The method involves an oxidation step of oxidizing the alkyl-aromatic compound to produce a first oxidation product. The initial oxidation process may be performed according to any known method of oxidizing alkyl-aromatic compounds, including, but not limited to, those described in the above patent documents and applications, or the methods described herein.

The second step involves contacting at least a portion of the first oxidation product with a solvent comprising an ionic liquid, a bromine source, a catalyst, and an oxidizing agent to form a solution comprising at least one of an aromatic alcohol, an aromatic aldehyde, an aromatic ketone, and an aromatic carboxylic acid To produce a second oxidation product.

The contacting step (s) can be performed up to commercial size manipulations in laboratory scale experiments. The process may be carried out in a batch, continuous or semi-continuous manner. The contacting step can be carried out in various ways. The order of addition of the components (e.g., first oxidation product, solvent, bromine source, catalyst, and oxidant) is not critical. For example, the components may be added separately, or the two or more components may be combined or blended with other components before mixing.

1 is a general process flow diagram for one embodiment of a process for preparing purified alkylaromatic aromatic compounds.

Any kind of process may be used in the first reaction zone. For example, any of the commercially available methods discussed in the patent literature cited above or elsewhere may be used if desired. The feed 200, including the oxidant 215 if present, enters the first reaction zone 210. The overhead condenser 225 can regulate the reaction zone temperature by removing heat from the reflux stream and the absorption zone 230 and dehydration zone 235 can remove offgas and water from the reaction zone.

The product from the first reaction zone is used as the feed 240 for the second oxidation reaction zone 245. The feed to the second oxidation reaction zone 245 also includes an oxidant 250 and a recycled ionic liquid stream 260. The ionic liquid solvent stream 260 may comprise a make-up ionic liquid 265 as well as a recovered ionic liquid.

The solvent in the second oxidation reaction zone 245 may include a carboxylic acid solvent and at least one ionic liquid. In comparison with conventional methods, when an ionic liquid is used, the amount of carboxylic acid solvent is reduced to prevent excessive solvent volume.

The overhead condenser 270 removes heat from the reflux stream of the second oxidation reaction zone 245 to regulate the reactor temperature and the absorption zone 275 and dehydration zone 280 remove off gases and water from the reaction zone do.

The second oxidation reaction zone 245 includes a stream 285 that returns to the second oxidation reaction zone 245 after the heat exchanger 290. Depending on the reaction zone design, the cooler recycle stream may be returned to the appropriate location in the vapor space, or plug-flow reaction zone, which is the upper stage of the reaction zone.

The effluent mixture 295 from the second oxidation reaction zone 245 is sent to the crystallization zone 300 to complete the crystallization process. The crystallization zone 300 may comprise at least one post-reaction zone and / or at least one crystallizer. If additional post-reaction zones are required to increase the conversion, additional oxidant may be required. The reaction zone may operate at lower pressure and lower temperature to assist in crystallization. One or more crystallizers are used to complete the crystallization of terephthalic acid at a lower temperature. Care should be taken not to co-crystallize the impurities. The solvent comprising the ionic liquid reduces impurities that are substantially co-crystallized by providing a medium in which impurities and / or intermediates remain in the solvent or are further oxidized to terephthalic acid.

 The crystallized product is separated from the solvent in the separation zone 305. The separation zone 305 may comprise one or more of a filter, a centrifuge, and a dryer, as is known in the art.

The solvent 310 is used to clean the product crystals in the separation zone 305. The purified product 315 is dried and stored in a product silo. Additional separation equipment may be required to ensure that the product meets product specifications prior to storage.

The washed mother liquor 320 is sent to the solvent separation zone 325. The ionic liquid 260 is recycled back to the second oxidation reaction zone 245 and optionally the first oxidation reaction zone is used in the first reactor depending on the process. Makeup ionic liquid 265 may be added as needed.

Catalyst 330 is sent for catalyst recovery.

The carboxylic acid solvent (335) is dehydrated in the dehydration zone (340). The carboxylic acid solvent (205) may be recycled back to the first oxidation reaction zone (210). Make-up carboxylic acid solvent 220 may be added if desired. The wastewater 345 is removed.

The first and second reaction zones may be present in different reactors if desired.

Suitable alkylaromatics or feeds to be oxidized include aromatic compounds comprising at least one benzene ring having at least one alkyl group. The methyl, ethyl, and isopropyl alkyl groups are preferred alkyl groups, but are not required. In one embodiment, the alkylaromatic compound is selected from toluene, p-xylene, o-xylene, and m-xylene. The feed may comprise more than one alkylaromatic compound. As the oxidation reaction proceeds generally through successive stages of oxidation, suitable feed compounds also include partial oxidation intermediates for the desired oxidation products. For example, in the preparation of terephthalic acid, the alkylaromatic feed may comprise p-toluic acid and / or 4-carboxybenzaldehyde (4-CBA).

The solvent comprises at least one ionic liquid. Two or more ionic liquids may be used if desired.

Generally, an ionic liquid is a non-aqueous organic salt consisting of ions in which the cation balances the charge with the anion. This material has a low melting point, mainly below 100 ° C, an undetectable vapor pressure, and excellent chemical and thermal stability. The cation charge of the salt is localized across heteroatoms, and the anion can be any inorganic, organic, or organometallic species.

Most ionic liquids are generated from cations that do not contain acidic protons. The synthesis of ionic liquids can generally be divided into two parts: the production of certain cations, and the anion exchange to produce the desired product. Quaternization of, for example, amines or phosphines is an early step in the cationic synthesis of ionic liquids. If the desired anion can not be directly produced by the quaternization reaction, an additional step is required.

A simple ion combination for producing an ionic liquid is estimated at hundreds of thousands, and the number of possible ionic liquid mixtures is nearly infinite (10 ¹⁸ ). This means that by selecting the anion concentration, the cation concentration, and the mixed concentration, the ionic liquid having a predetermined characteristic should be designed for a specific application field. Ionic liquids may be adjusted or adjusted to provide specific melting points, viscosities, densities, hydrophobicity, miscibility, etc., for particular applications. The thermodynamics and kinetics of the processes performed in ionic liquids are different from those in conventional media. This creates new opportunities for contact reactions, separation, reaction / separation combination processes, heat transfer agents, hydraulic fluids, paint additives, electrochemical applications and many others. Ionic liquids do not emit volatile organic compounds (VOCs) and thus provide the basis for clean manufacturing, for example, "green chemistry ".

The organic cation may include linear, branched, or cyclic heteroalkyl units. The term "heteroalkyl" refers to a cation that contains at least one heteroatom selected from nitrogen, oxygen, sulfur, boron, arsenic, boron, antimony, aluminum, or phosphorus capable of generating a cation. A heteroatom may be part of a ring formed with one or more other heteroatoms, such as a pyridinyl, imidazolinyl ring, which rings may have a substituted or unsubstituted linear or branched alkyl unit attached thereto have. In addition, the cation may be a single heteroatom, wherein a sufficient number of substituted or unsubstituted linear or branched alkyl units are bonded to the heteroatom such that the cation is produced.

Non-limiting examples of heterocyclic and heteroaryl units that can be alkylated to produce cationic units include imidazole, pyrazole, thiazole, isothiazole, azathiazole, oxothiazole, oxazine, Isothiazole, isothiazole, tetrazole, thiophene, thiophene, thiophene, indole, oxazole, oxazole, Benzothiophene, dibenzothiophene, thiadiazole, pyridine, pyrimidine, pyrazine, pyridazine, piperazine, piperidine, morpholine, pyran, annoline, Phthalazine, quinazoline, and quinoxaline.

The anion portion of the ionic liquid may comprise an inorganic, organic, or organic metal moiety. Non-limiting examples of anions include inorganic anions: halogen, (e.g., F, Cl, Br, and I); Boride, BX ₄ (wherein X represents a halogen (e.g., BF ₄ , BCl ₄ ), etc.); Phosphate (V), PX ₆ ; PF _6, etc .; Arsenate (V), AsX ₆ ; AsF _6, etc .; Stibate (V) (antimony), SbX ₆ ; SbF ₆ and the like; CO ₃ ^2- , NO ₂ ^1- , NO ₃ ^1- , SO ₄ ^2- , PO ₄ ^3- , (CF ₃ ) SO ₃ ^1- .

Other non-limiting examples of ionic liquid anions include substituted azolates, i.e., 1 and 3 positions (imidazolylate); 1, 2, and 3 positions (1,2,3-triazololate); Or a 5-membered heterocyclic aromatic ring having nitrogen atoms at 1,2,4-position (1,2,4-triazolate). Substitution of a ring is a CN (cyano-) bonded to the heterocyclic azole rate core taking place in the position not located in the N position (which is carbon position) comprises a, and NH ₂ (amino), NO ₂ (nitro) do.

Further non-limiting examples of anions include substituted or unsubstituted borides: B (R < ¹⁰ >) ₄ ; Substituted or unsubstituted sulfates: (RO) S (= O) ₂ O; Substituted or unsubstituted acyl units RCO ₂ , such as acetate CH ₃ CO ₂ , propionate, CH ₃ CH ₂ CO ₂ , butyrate CH ₃ CH ₂ CH ₂ CO ₂ , and benzylate, C ₆ H ₅ CO ₂ ; Substituted or unsubstituted phosphate: (RO) ₂ P (= O) O; Substituted or unsubstituted carboxylate: (RO) C (= O) O; Substituted or unsubstituted azolates wherein the azolate may be substituted on the carbon atom by a unit selected from cyano, nitro, and amino. R can be an organic, inorganic, or organometallic group. Non-limiting examples of R are hydrogen; Substituted or unsubstituted linear, branched, and cyclic alkyl; Substituted or unsubstituted linear, branched, and cyclic alkoxy; Substituted or unsubstituted aryl; Substituted or unsubstituted aryloxy; Substituted or unsubstituted heterocyclic; Substituted or unsubstituted heteroaryl; Acyl; Silyl; Boryl; Phosphino; Amino; Thio; And seleno.

In one embodiment, the ionic liquids suitable for use include, but are not limited to, one or more of an imidazolium ionic liquid, a pyridinium ionic liquid, a tetraalkylammonium ionic liquid, and a phosphonium ionic liquid. More than one ionic liquid may be used. The imidazolium, pyridinium, and ammonium ionic liquids have a cation containing at least one nitrogen atom. Phosphonium ionic liquids have cations containing one or more phosphorus atoms. In one embodiment, the ionic liquid comprises a cation selected from alkyl imidazolium, di-alkyl imidazolium, and combinations thereof. In another embodiment, the ionic liquid comprises anions selected from halides, acetates, carboxylates, and combinations thereof. The ionic liquid may be selected from the group consisting of 1-butyl 3-methyl imidazolium acetate (BMImOAc), 1-butyl 3-methyl imidazolium bromide (BMImBr), 1-hexyl 3-methyl imidazolium acetate, Imidazolium < / RTI > bromide.

The ionic liquid may be supplied, or it may be generated in situ from a suitable precursor, or both. When an ionic liquid is produced in situ, the solvent comprises a precursor of at least one ionic liquid. Ionic liquid precursors include cationic precursors such as alkylimidazoles, alkylpyridines, alkylamines, alkylphosphines, and the like, and anionic precursors such as alkyl or aryl halides or acetates. In one embodiment, the precursors are methyl imidazole and butyl bromide.

The manner of introducing the ionic liquid precursor may vary depending on the nature of the alkylaromatics to be oxidized and the nature and purity of the desired product. In one mode of addition, the cation precursor and the anion precursor (generally liquid at room temperature and pressure) are mixed with a carboxylic acid (e.g., acetic acid) solvent and then introduced into the oxidation reactor (s). In another mode of addition, the ionic liquid precursor may be introduced into the oxidation reactor after mixing with the alkyl aromatic feed. In another mode of addition, both the cationic and anionic ionic liquid precursor components are introduced into the bottom of the reactor without premixing with any other oxidation reactor components such as feed, carboxylic acid solvent, and catalyst package .

The solvent may also include a carboxylic acid. When a carboxylic acid is used in a solvent, the amount of the carboxylic acid is reduced as compared with the conventional method in order to prevent excessive solvent volume. The carboxylic acid preferably has 1 to 7 carbon atoms. In one embodiment, the carboxylic acid comprises acetic acid. The solvent may contain more than one carboxylic acid. For example, the solvent may further comprise benzoic acid. In another embodiment, the acid of the solvent is acetic acid.

In one embodiment, the solvent is selected from the group consisting of 1:16 to 16: 1, or 1: 9 to 9: 1, or 3: 1 to 17: 3, or 1: 4 to 4: , Or 3: 7 to 7: 3, or 7: 13 to 13: 7, or 2: 3 to 3: 2, or 9:11 to 11: 9, or 1: 1 carboxylic acid to ionic Liquid < / RTI > In one embodiment, the solvent comprises more than 5% by weight of an ionic liquid, or 6% by weight or more of an ionic liquid, or 10% by weight or more of an ionic liquid, or 15% Or 25 wt.% Or more of an ionic liquid, or 30 wt.% Or more of an ionic liquid, or 35 wt.% Or more of an ionic liquid, or 40 wt.% Or more of an ionic liquid, or 45 wt. The amount of ionic liquid, if present, comprises an ionic liquid precursor. Any ionic solid or material capable of producing an ionic salt in solution, as described below, is included in the amount of ionic liquid, if present.

Optionally, ionic solids, such as ammonium acetate (NH ₄ OAc) and / or ammonium bromide (NH ₄ Br) may be added to the mixture. Alternatively, a material capable of producing an ionic salt in solution may be added. The material can be combined with the ions present in the solution to produce an ionic salt in solution. For example, in a solution containing a bromide ion (in the form of HBr, for example) or an acetate ion (e.g. in the form of acetic acid), ammonia is combined with the bromide or acetate ion to produce ammonium bromide or ammonium acetate can do. The use of one or more ionic solids or materials capable of producing ionic salts in a solution provides a further reduction of the impurity level.

In one embodiment, the amount of ionic solid and / or material capable of producing an ionic salt in solution is from 5% to 45% by weight, or from 10% to 45% by weight, based on the weight of the solvent, %. Solvents include carboxylic acids, ionic liquids and / or ionic liquid precursors, any ionic solid or material capable of producing ionic salts in solution, and any water.

Optionally, the solvent further comprises water. Water may be added to the mixture or may be produced in the mixture during the oxidation process. In one embodiment, the amount of water ranges from 0.01 wt% to 5 wt%, based on the weight of the carboxylic acid. The amount of water may range from 0.1 wt% to 2 wt% based on the weight of the carboxylic acid.

In one embodiment, the weight ratio of solvent to alkyl-aromatic compound in the mixture ranges from 1: 1 to 10: 1, or from 1.5: 1 to 6: 1, or from 2: 1 to 4: Solvents include carboxylic acids, ionic liquids and / or ionic liquid precursors, any ionic solid or material capable of producing ionic salts in solution, and any water.

The catalyst includes at least one of cobalt, manganese, titanium, chromium, copper, nickel, vanadium, iron, molybdenum, tin, cerium and zirconium. In one embodiment, the catalyst comprises cobalt and manganese. The metal may be in the form of an inorganic or organic salt. For example, metal catalysts may be in the form of carboxylic acid salts, such as metal acetates and hydrates thereof. Exemplary catalysts include cobalt (II) acetate tetrahydrate and manganese (II) acetate, either individually or in combination. In one embodiment, the amount of manganese (II) acetate is less than the amount of cobalt (II) acetate tetrahydrate by weight.

The amount of the catalyst used in the present invention may vary greatly. For example, the amount of cobalt may range from 0.001 wt% to 2 wt%, based on the weight of the solvent. In one embodiment, the amount of cobalt ranges from 0.05 wt% to 2 wt%, based on the weight of the solvent. The amount of manganese may range from 0.001 wt% to 2 wt% based on the weight of the solvent. In one embodiment, the amount of manganese ranges from 0.05 wt% to 2 wt%, based on the weight of the solvent. In another embodiment, the weight ratio of cobalt to manganese ranges from 3: 1 to 1: 2, based on the elemental metal.

Bromine source and is generally known in the art to be a catalyst promoter, bromine, ionic bromide, for example HBr, NaBr, KBr, NH ₄ Br; Organic bromides such as benzyl bromide, monobromoacetic acid, and dibromoacetic acid, bromoacetyl bromide, tetrabromoethane, and ethylene di-bromide, which are known to provide bromide ions under oxidative and / or oxidative conditions. In one embodiment, the bromine source comprises hydrogen bromide, or consists essentially of hydrogen bromide. The amount of hydrogen bromide may range from 0.01 wt% to 5 wt% based on the weight of the solvent. In another embodiment, the amount of hydrogen bromide ranges from 0.05 wt% to 2 wt%, based on the weight of the solvent. Solvents include carboxylic acids, ionic liquids and / or ionic liquid precursors, any ionic solid or material capable of producing ionic salts in solution, and any water.

Oxidizing agents suitable for the present process provide a source of oxygen atoms to oxidize p-xylene and / or p-toluic acid, and / or another intermediate oxidation product under the oxidizing conditions employed. Examples of the oxidizing agent include peroxide, excess oxide, and a nitrogen compound containing oxygen, such as nitric acid. In one embodiment, the oxidizing agent is a gas comprising oxygen, such as air, carbon dioxide, and molecular oxygen. The gas may be a mixture of gases. The amount of oxygen used in the process preferably exceeds the stoichiometric amount required for a given oxidation process. In one embodiment, the amount of oxygen in contact with the mixture ranges from 1.2 times the stoichiometric amount to 100 times the stoichiometric amount. Optionally, the amount of oxygen in contact with the mixture may range from two times the stoichiometric amount to thirty times the stoichiometric amount.

At least one of the components can not be completely dissolved during any or part of the process, but at least some of the components provide a liquid phase. The liquid phase may be formed by mixing the components in ambient conditions. In another embodiment, a liquid phase is formed as the temperature of the mixture increases to the oxidation temperature. The mixture of components may be formed in the same or different vessel than that used in the oxidation step prior to the oxidation step. In another embodiment, the mixture of components is formed in an oxidation reactor, for example, by adding various streams of components individually and / or in combination to a continuous or semi-continuous oxidation reactor. The combined components, and / or the various streams of components may be heated before mixing together.

Many conventional alkylaromatic oxidation processes are typically performed in a mixed phase and often include three phases (e.g., solids, gases, and liquids), which are often referred to in the art as "liquid phase" Because the conditions are maintained to provide at least a portion of the mixture in liquid phase. It is also known in the art that the number of phases present can change with time in the process. The process according to the invention can also be carried out in liquid or mixed form in a manner analogous to those known in the art.

The present invention may be practiced using conventional liquid phase oxidation reactors such as those known in the art. Examples include containers capable of having at least one mechanical stirrer, and various bubble column reactors, such as those described in US 7,692,036. It is also known to design, conduct, and control the oxidation reactions for these reactors and the oxidizing conditions used, including, for example, temperature, pressure, liquid and gas volume, and, if applicable, liquid and gaseous corrosion characteristics have. See, for example, US 7,692,036 and US 6,137,001.

The contacting step (s) can be carried out under oxidizing conditions if necessary. Suitable oxidation conditions generally include a temperature in the range of 125 캜 to 275 캜, and atmospheric pressure, i.e., a pressure in the range of 0 MPa (g) to 6 MPa (g) and a residence time in the range of 5 seconds to 2 weeks. That is, the mixture may have a temperature and pressure within that range and be maintained within that range for a time within the residence time range. In another embodiment, the temperature ranges from 175 [deg.] C to 225 [deg.] C; The temperature may range from 190 캜 to 235 캜. In one embodiment, the pressure ranges from 1.2 MPa (g) to 6.0 MPa (g); The pressure may range from 1.5 MPa (g) to 6.0 MPa (g). In a further embodiment, the residence time ranges from 10 minutes to 12 hours. The oxidation temperature, pressure and residence time may vary based on various factors including, for example, reactor configuration, size, and whether the process is batch, continuous, or semi-continuous. The oxidation conditions may also vary based on different oxidation conditions. For example, the use of a particular temperature range may allow different residence time ranges to be used.

In one embodiment, the terephthalic acid produced by the present invention can precipitate, crystallize, or solidify in the liquid phase mixture under oxidizing conditions and / or as the reaction mixture cools. Thus, the mixture according to the present invention may further comprise solid terephthalic acid. Other compounds, including color bodies, and other oxidation products can be solidified with the solid oxidation product or trapped in the solid oxidation product to reduce the purity of a given product. In one embodiment, the mixture comprises a liquid phase. The mixture may comprise a gaseous phase, for example when the oxidizing agent is added to the gas. The mixture may comprise a by-product which is not soluble in the solid phase, e. G., The mixture component, the oxidation product, or the mixture, or is solidified in the mixture. In one embodiment, the mixture comprises a liquid phase, a solid phase and an arbitrary vapor phase. In another embodiment, the mixture comprises a liquid phase and a vapor phase.

As noted above and discussed below, it has been found that the present invention can be used to produce oxidation products with different amounts of contaminants as compared to those observed in conventional processes. Additionally, the present invention provides a novel method of controlling the level of various contaminants in the oxidation products. In one embodiment, the process according to the present invention further comprises a step of producing an oxidation product to a solid, optionally under oxidizing conditions, to produce a solid oxidation product and a mother liquor. The solid oxidation product can be separated from the mother liquor, that is, the liquid and mother liquor of the process can be recycled and reused in the contacting step or other steps of the process described below.

The methods according to the present invention may comprise one or more additional oxidation steps. In one embodiment, the second oxidation step comprises a second oxidation temperature that is lower than the temperature of the first oxidation step. The methods according to the present invention may include the additional contacting step of the invention described herein and / or the invention may be combined with other oxidation steps, for example conventional oxidation steps known in the art. Multiple contact and / or oxidation steps may be performed in series and / or in parallel and may be combined with other processing steps, such as the purification steps described herein.

In another embodiment, the present invention further comprises purifying the oxidation product. The purification step may comprise one or more additional steps of isolating and purifying the oxidation product. Examples of purification steps include: a separation step in which the oxidation product is separated from the mother liquor or another liquid phase by, for example, filtration and / or centrifugation; A washing step in which the oxidation product is washed with, for example, water and / or another solvent component; Drying the oxidation product; And a hydrogenation process. Hydrogenation processes can be used for purification, but this is less desirable than other purification methods due to cost. These additional processing steps are described in the general literature and are well known to those skilled in the art and are used in various combinations for purifying the oxidation products of the present invention. For example, reference is made to the references cited in this application and to the art quoted herein.

The purification step of the present invention may further comprise at least one solvent contacting step. The solvent contacting step may comprise contacting the oxidation product, which also includes the washed or dried solid oxidation product, with a third solvent comprising at least one of water, a carboxylic acid, an ionic liquid and / or an ionic liquid precursor, and a mother liquor And a contacting step of producing a purified oxidation product. In one embodiment, the solvent in the solvent contacting step contains an ionic liquid and a carboxylic acid, and any mother liquor. The composition of the solvent for the solvent contacting step may be as described above for the contacting step.

The solvent contacting step may leach impurities from the solid oxidation product and / or the oxidation product may be partially or completely dissolved in the solvent. The solvent contact conditions include the solvent contact temperature. The solvent contact temperature may be lower than the oxidation temperature. In one embodiment, the solvent contact temperature may be at least 20 DEG C lower than the oxidation temperature. The solvent contacting step may be carried out, for example, in one or more crystallisers following an oxidation reactor in some conventional processes. The oxidation product can be solidified, precipitated, or crystallized in the solvent of the solvent contacting step.

The product produced by the present process may be initially treated with less than 2500 ppm of 4-CBA, or less than 2000 ppm of 4-CBA, or less than 1500 ppm of 4-CBA , Or less than 4 ppm of 4-CBA, or less than 750 ppm of 4-CBA, or less than 500 ppm of 4-CBA, or less than 250 ppm of 4-CBA, or less than 100 ppm of 4-CBA, Of 4-CBA, or less than 25 ppm of 4-CBA.

It should be noted that the terms "first "," second ", and "third ", etc. are used to distinguish one component, or composition, or step, or zone, or reactor, The "second" step or zone does not have to follow the "first" step or zone, e.g., physically or temporally. Depending on the circumstances, as understood by those skilled in the art, this may be before or after.

While one or more exemplary embodiments are set forth in the foregoing description of the invention, it should be understood that there are numerous variations. It is also to be understood that the exemplary embodiment (s) is illustrative only and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a simplified road map for implementing the exemplary embodiments of the invention. It will be understood that various changes may be made therein without departing from the scope of the invention as set forth in the appended claims, to the action and function of the components described in the exemplary embodiments.

Claims (10)

A method of oxidizing an alkyl-aromatic compound,
Oxidizing the alkyl-aromatic compound to produce a first oxidation product;
Contacting at least a portion of the first oxidation product with a solvent comprising an ionic liquid, a bromine source, a catalyst, and an oxidizing agent to form a second solution comprising an aromatic alcohol, an aromatic aldehyde, an aromatic ketone, and an aromatic carboxylic acid, Contact stage to produce oxidation product
≪ / RTI > 3. The method of claim 1, further comprising contacting the at least a portion of the second oxidation product with a second solvent comprising a second ionic liquid to produce a third oxidation product. 3. The method of claim 2 wherein the temperature of the second contacting step is lower than the temperature of the first contacting step. 4. A process according to any one of claims 1 to 3, wherein the contacting of the second oxidation product is carried out under oxidizing conditions in the presence of a second oxidant and a second catalyst. The method of claim 1, wherein the oxidation step and the contacting step are performed in a reaction zone. The method of claim 1 wherein the oxidation step is performed in a first reaction zone and the contacting step is performed in a second reaction zone. 7. The process of claim 6, wherein the first reaction zone and the second reaction zone are in different reactors. The method of any one of claims 1, 5, 6, and 7, further comprising purifying the second oxidation product. The method of any one of claims 1, 5, 6, and 7, wherein the ionic liquid is generated in situ from at least one ionic liquid precursor. The method of any one of claims 1, 5, 6, and 7, wherein the contacting step further comprises adding a substance capable of producing an ionic solid or ionic salt Way.

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